Phagocytosis of promastigotes and amastigotes of Leishmania mexicana by the FSDC dendritic cell line: Ultrastructural study

Abstract

Introduction. Dendritic cells, which capture and present antigen to activate unprimed T cell, arefound in most tissues.Objective. This work describes the ultrastructure of Leishmania mexicana phagocytosis by thefetal skin dendritic cell (FSDC) line, a Langerhans cell line isolated from mouse fetal epidermisimmortalized by retroviral transduction of the v-myc oncogene.Materials and methods. Leishmania amastigotes were obtained from mouse (BALB/c) lesionand promastigotes from culture (24°C) of the lesion. FSDC cells were cultured with parasites (5parasites per cell) using IMDM medium, during 24 hours. Control and infected cultures wereprocessed for transmission electron microscopy. Semi-thin sections counterstained with toluidine blue to evaluate phagocytosis and thin sections counterstained with uranyl acetate and leadcitrate were made.Results. 13.42% of the FSDC phagocytosed promastigotes; 8% contained a single parasiteand 5.2% phagocytosed 2 or more. 20% of the FSDC phagocytosed amastigotes; 10% containeda single parasite and 10% phagocytosed 2 or more. Ultrastructurally, promastigotes in contactwith FSDC by the flagellum or the posterior pole were observed. The parasitophorous vacuolesharbouring promastigotes were small organelles containing one or two parasites each.Parasitophorous vacuoles containing amastigotes were larger (8μm diameter) with one orseveral parasites free or attached to the vacuole at the posterior pole.Conclusion. The low rate of infected FSDC cells was characteristic and the parasitophorousvacuole showed similar characteristics to those observed in macrophages. The parasite densityin the infected cells was 1 to 3 parasites per cell. These observations highlight the need to studythe relationship between phagocytic capacity and function.